1. Field of the Invention
The present invention relates to an image noise reduction method. More particularly, the present invention relates to an image noise reduction method based on an optimal primary-color signal.
2. Related Art
The shooting quality of a digital camera is dependent upon the photosensitivity of a photosensitive element, such as charge coupled device (CCD), complementary metal-oxide semiconductor (CMOS). However, when the digital camera shoots in a high ISO mode, image noises are unavoidably generated, which are generally spots distributed randomly. Currently, many digital cameras have noise reduction function to reduce the noises of the shot image when the digital camera is in the high ISO mode. Most of the current image-sensing elements have different sensitivities for different primary colors, or they may need a white balance treatment due to the influences of the color of the ambient lights, and the gain compensation is applied to each primary color after taking out the signal, such that each primary color achieves optimal signal strength. However, due to the different gain compensations for the primary colors, the amplification ratios of the noises are different for the primary-color signals. The greater the gain is, the greater the noises of the primary are. In order to make the signal-to-noise ratio of the worse primary color to approach that of the better primary color as much as possible, an algorithm of removing the noises in the color difference domain has been proposed in the part. According to the algorithm, with the optimal primary-color signal as a center, a difference value from other primary-color signals are generated, and then a fuzzy operation or a neutralization operation is performed on the difference values, and finally the difference value is restored.
However, the method of processing the noises of the digital image based on the color difference domain still faces the problem that the image details cannot be reserved due to improper treatments on the image characteristics. Especially, when the noises are rather large, the reservation of the image details becomes extremely difficult. If the image details are required to be reserved, a great deal of computations is generally needed. Merely for the noise reduction in the color difference domain, the effect for improving the image noises is limited.